<!DOCTYPE html>

<html>

<head lang="en">
  <meta charset="UTF-8">
  <title></title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    table {
      border-collapse: collapse;
      border-spacing: 0;
      border: 1px solid #c0c0c0;
      width: 500px;
      margin: 100px auto;
      text-align: center;
    }

    th {
      background-color: #09c;
      font: bold 16px "微软雅黑";
      color: #fff;
      height: 24px;
    }

    td {
      border: 1px solid #d0d0d0;
      color: #404060;
      padding: 10px;
    }

    .allCheck {
      width: 80px;
    }

    /* input:checked{
      width: 100px;
      height: 100px;
      border: 2px red solid;
    } */
  </style>
</head>

<body>
  <table>
    <tr>
      <th class="allCheck">
        <input type="checkbox" name="" id="checkAll"> <span class="all">全选</span>
      </th>
      <th>商品</th>
      <th>商家</th>
      <th>价格</th>
    </tr>
    <tr>
      <td>
        <input type="checkbox" name="check" class="ck">
      </td>
      <td>小米手机</td>
      <td>小米</td>
      <td>￥1999</td>
    </tr>
    <tr>
      <td>
        <input type="checkbox" name="check" class="ck">
      </td>
      <td>小米净水器</td>
      <td>小米</td>
      <td>￥4999</td>
    </tr>
    <tr>
      <td>
        <input type="checkbox" name="check" class="ck">
      </td>
      <td>小米电视</td>
      <td>小米</td>
      <td>￥5999</td>
    </tr>
  </table>
  <script>
    // 全选框
    let all = document.querySelector(`.allCheck input`);
    // 小复选框
    let check = document.querySelectorAll(`.ck`);
    // 给全选框，添加点击事件
    all.addEventListener(`click`, function () {
      // 先看下全选框的状态
      // console.log(this.checked);  // true false
      for (let i = 0; i < check.length; i++) {
        check[i].checked = this.checked;
      }
    })

    console.log(document.querySelectorAll(`.ck:checked`).length);

    // 给小复选框添加点击事件，并且判断选中的小框的总个数是不是等于小复选的总个数
    // 判断有几个小复选框被选中
      for (let i = 0; i < check.length; i++) {
        check[i].addEventListener(`click`,function(){
          all.checked=document.querySelectorAll(`.ck:checked`).length==check.length
        })
    }
  </script>
</body>
</html>